As well known to those skilled in the art, a moiré device is commonly used to measure the three-dimensional shape of an object. As disclosed in Korean Patent Laid-open Publication No. 98-7797, a conventional phase-shifting projection moiré device measures a three-dimensional shape using a projection grid 513 and reference grid 512. Namely, by moving the projection grid 513 and reference grid 512, during a measurement, with their grid images being formed as shown in FIG. 1b using a semiconductor lithography technique on a quartz glass, various moiré images can be obtained so as to achieve an information about the three-dimensional shape from these images.
A conventional projection moiré device to which the above technique is applied will be described with reference to FIG. 1a. A beam of light from a white light source 510 is condensed through a condenser lens 516 and then projected to an object to be measured 515 through a projection grid 513 and projection lens 517, forming a grid image of line patterns on the object, which is deformed corresponding to the three-dimensional shape of the object, as shown in FIG. 1c. The deformed line pattern image is focused on an image pickup surface of a CCD camera 511 after being passed through an image formation lens 518, reference grid 512 and relay lens 519. An image obtained as a result is shown in FIG. 1d, wherein the resulting image is synthesized during time that the deformed line pattern image, that is a cast of the projection grid, is passed through the reference grid 512.
The resulting image is synthesized from the line pattern moiré image having the information of the three-dimensional shape of the object 515 and an image of the reference grid, wherein the reference grid image is a main cause of measurement error, whereby additional specific equipment is commonly used to remove the reference grid image from the synthesized image.
To measure a three-dimensional shape using the conventional moiré device, it is necessary to adjust a distance between line patterns of the line pattern image in accordance with measurement parameters such as the size of an object to be measured, topology, accuracy of measurement or the like, so the conventional device for measuring a three-dimensional shape needs various kinds of projection grids and reference grids. Thus, the conventional device is inconvenient in that the projection grid and reference grid have to be changed every time in accordance with an object to be measured, as well as having a high manufacturing cost.
The conventional device for measuring a three-dimensional shape must have an additional moving unit 514 to move the projection grid and reference grid a minute distance in order to obtain various moiré images, thereby having problems of enlarging a volume of equipment and increasing a manufacturing cost.